This invention generally relates to an apparatus for detecting data of a signal reproduced from an optical disk, and particularly relates to an apparatus for controlling a data detecting signal in an optical-disk data detecting system.
Some optical disks have recording tracks in which servo regions and data recording regions are alternately arranged in series. Information signals for servo control are previously recorded into the servo regions while data can be recorded into the data recording regions.
Such optical disks contain magneto-optic disks of the sampling servo type. In a magneto-optic disk of the sampling servo type, there inevitably occurs a phase difference between pits previously recorded in the servo regions and data of pits recorded in the data recording regions. In general, reproducing/recording systems for disks of this type are adjusted so as to minimize such a phase difference before being forwarded from a factory.
Japanese published unexamined patent application 63-244448 discloses a system for an optical disk. In the system of Japanese application 63-244448, during the recording of data, data detecting sync signals are also recorded into predetermined ones of the data recording regions of the optical disk. In addition, during the reproduction of the data from the optical disk, a data detecting signal for determining the timing of detection of the data is generated on the basis of the data detecting sync signals to realize a good recovery of the data.
The system of Japanese application 63-244448 includes a variable delay line which controls the delay amount of the data detecting signal so that sample values of signals reproduced from the servo regions and sample values of the data detecting sync signals reproduced from the data recording region will be equal in magnitude. In the system of Japanese application 63-244448, a close relation is not ensured between the equality of the magnitudes of the two sample signals and the nullification of a phase difference for various reasons such as a reason related to the use of different detecting devices for the two signals respectively, and a reason related to the dependence of the recording and reproducing levels of signals upon the sensitivity of an optical disk. In the system of Japanese application 63-244448, when the levels of the two signals are different from each other, there is no information representing which of the two signals should be delayed by the signal delay line and thus good servo control tends to be difficult. In the system of Japanese application 63-244448, when the envelopes of the reproduced data detecting sync signals are varied by low-cut characteristics of a signal transmission part of the system, good servo control can not be expected.